Some starter TeX resources

TeX (and its newer variation LaTeX) is the system that allows you to typeset mathematics.
In some sense, TeX is a programming language -- you have to create your file (with text as usual, but all mathematical symbols defined by commands) using some text editor.
Then you compile your file, and the result is the pdf file with beautifully typeset mathematical document (for example, homework). So, in principle, you will need to install the TeX compiler on your computer, and use some text editor (some are better suited for TeX than others).
However, to start with, it is probably best to use a wonderful new cloud tool for creating LaTeX documents.

Writelatex.com .
It allows you NOT to install anything on your computer, but to create documents online, and then print them out at the end.Your document is given a special link, so when you stop your work, you can save the link, and then return to your document later just by pasting that link into your borwser.
The only downside is that if you are creating homework that way, you will be able to work on it only when you have internet connection. But this is probably the best place to start.

Here is a document sample -- the source files (in LaTeX) of the first
Math 220 handout:

The source for the handout on subsets .
To create a TeX document, you can take this file, open it with your
favourite
text editor,
leave the top few lines as is, and then just put your work between
\begin{document} and \end{document}. To use this option, you will need to
have TeX installed on your computer.